When Anomo’s 300,000 users this week begin to post the hashtag #Vegas, a native-style ad will appear. “Traveling here is about having an experience you cannot get at home,” said Dustin Robertson, CMO at the Sin City bookings site. “So much of our traffic is coming from mobile that if we can get into people’s phones, that’s a market we are willing to pay for.”

Vegas.com is far from alone. MTV last week unveiled a campaign on Whisper, joining additional newcomers Hulu and Universal Pictures. Whisper is gaining momentum. The app claims 6 billion monthly pageviews, with the average user opening the app 10 times for a total of 30 minutes daily.

Whisper as well as its buzzy rival Secret, which has not yet begun to develop ads, say that marketers routinely inquire about pay-for-play opportunities as they’re intrigued by connecting to targeted users.

Not everyone sees the light on dark social. Harley Block, brand development svp at agency Rokkan, predicted some marketers will wait until there is more scale. But he also hinted that anonymous platforms do have a Vegas kind of appeal.

“Brands,” he said, “can have a little more freedom here to experiment [than] in a real-world environment.”